1. Field of the Invention
This invention relates to a transmitting method, a receiving method, a communication method, and a bi-directional bus system, which are used in a system in which devices, e.g., a televisionimage receiver or a video tape recorder, etc. are connected to each other by using a bi-directional bus to control, from otherdevices, sub-devices, e.g., a monitor image receiver, a TV tuner, or a video deck, etc. included in the devices, or to display the operating states, etc. of other devices on the television image receiver.
2. Description of the Related Art
In recent years, there have been popularly used systems in which a plurality of audio equipments or visual equipments (hereinafter referred to as AV equipments) are connected by means of video signal lines or audio signal lines (hereinafter referred to as AV signal lines).
In such AV systems, equipments are connected by means of a system control bus (hereinafter simply referred to as a bi-directional bus) in addition to the above-described AV signal lines to control respective equipments. In a practical sense, Audio, Video and audiovisual systems Domestic Digital Bus (hereinafter referred to as D2B) standardized by the so-called publication 1030 of IEC, a Home Bus System (hereinafter referred to as HBS) standardized by the ET-2101 of EIAJ, and the like are known. Through the bi-directional bus, other devices are controlled from equipments (devices), e.g., a television image receiver, a video tape recorder, and a video deck player (hereinafter respectively referred to as TV, VTR, VDP), etc., or sub-devices, e.g., a monitor image receiver (TV monitor), a TV tuner, a video deck, or an amplifier, etc. included in other devices are controlled from devices. Further, through the bi-directional bus, data for displaying, on a TV monitor, e.g., the operating state (status) of device or sub-device is transmitted. In addition, as an access system of the bi-directional bus, so called CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is employed in, e.g., D2B.
Namely, communication from a sub-device included in a device to a sub-device included in any other device (hereinafter referred to as communication from sub-device to sub-device), communication from a sub-device included in a device to any other device (hereinafter referred to communication from sub-device to device), communication from a device to a sub-device included in any other device (hereinafter communication from device to sub-device), and communication from a device to any other device are carried out through the bi-directional bus.
The format of a transmit signal used in a bi-directional bus as described above, e.g., D2B will now be described. In D2B, control commands for controlling a sub-device of destination (on the receiving side), etc. or data indicating the operating state, etc. are caused to have a frame configuration as shown in FIG. 1, and are transmitted through the bi-directional bus.
Namely, one frame consists of a header field 101 for specifying the header indicating the leading portion of the frame, a master address field 102 for specifying a source device address, a slave address field 103 for specifying a destination device address, a control field 104 for specifying a data communication command indicating communication of data or a control command communication command indicating communication of control command, and a data field 105 for specifying control command or data.
The header of the header field 101 consists of, as shown in FIG. 2, a start bit 101a of one bit for providing synchronization, and mode bits 101b for prescribing a transmission speed (rate) or the number of bytes of the data field 105. These mode bits 101b are 1.about.3 bits. At present, three modes of mode 0 where the data field 105 is comprised of 2 bytes at the maximum, mode 1 where the data field 105 is comprised of 32 bytes at the maximum (16 bytes at the maximum in the case of communication from slave to master), and mode 2 where the data field 105 is comprised of 128 bytes at the maximum (64 bytes at the maximum in the case of communication from slave to master) are standardized.
The source device address of the master address field 102 consists of, as shown in the above-mentioned FIG. 2, master address bits 102a of 12 bits for specifying a source device address, and a parity bit 102b of 1 bit.
The destination device address of the slave address field 103 consists of, as shown in the above-mentioned FIG. 2, a slave address bits 103a of 12 bits for specifying a destination device address, a parity bit 103b of 1 bit, and an acknowledge bit 103c of 1 bit for responding from a destination device.
To the control field 104, as shown in the above-mentioned FIG. 2, control bits 104a of 4 bits comprised of a data communication command indicating communication of data or a control command communication command indicating communication of control command, i.e., data communication command indicating that the control of the data field 105 is data and control command communication command indicating that it is control command, a parity bit 104b of 1 bit, and an acknowledge bit 104c of 1 bit are assigned.
In the data field 105, as shown in the above-mentioned FIG. 2, data bits 105a of 8 bits, end of data bit 105b of 1 bit, parity bit 105c of 1 bit, and acknowledge bit 105d of 1 bit are repeated as occasion demands. Assuming now that data bits 105a are assumed to be data #1, #2, #3, . . . in order from the beginning, in communication of, e.g., control command, e.g., Operation code (hereinafter referred to as OPC) "Begin 2" (i.e., code "BD"h (h represents hexadecimal number)) indicating communication relating to sub-device, OPC "Begin 1" ("BC"h) indicating communication through HBS, and OPC "Begin O" ("BB"h) indicating communication through other bus, etc. are assigned (allocated) to data #1. Further, e.g., in communication of data, data are assigned to data #1, #2 #3 . . . every byte (8 bits).
OPR with respect to the above-described OPCs, e.g., OPR with respect to OPC "begin 2" consists of, as shown in FIG. 3, bits b5, b4, b3, b2 (b7 is the Most Significant Bit (MSB) for identifying service codes of the Communication Telephony (CT) system, the Audio Video and Control (AV/C) system, and the Housekeeping (HK) system, etc.; and bits b1, b0 indicating any one of communication from sub-device to sub-device, communication from sub-device to device, communication from device to sub-device, and communication from device to device, viz., indicating presence or absence of Source Sub-Device Address (hereinafter referred to as SSDA) or Destination Sub-Device Address (hereinafter referred to as DSDA). It is to be noted that bit b7 is caused to be always zero, and bit b6 is reserved for future standardization and is caused to be 1 at present. In more practical sense, b1=0, b0=0 indicates communication from sub-device to sub-device; b1=0, b0=1 indicates communication from sub-device to device; b1=1, b0=0 indicates communication from device to sub-device; and b1=1, b0=1 indicates communication from device to device.
Now, in the case of transmitting data having a data quantity greater than a data capacity of the data field 105 from VTR to TV in a manner divided into a plurality of frames, VTR forms, as shown in FIG. 4A, a frames P1 in which master address bits are caused to be an address of VTR, slave address bits are caused to be an address of TV, control bits are caused to be a code "A"h indicating control communication command, and OPC "Begin 2", code "54" indicating presence of SSDA and DSDA, address of, e.g., of video deck, address of, e.g., TV monitor, code "EO"h indicating control of display, code "20"h indicating, e.g., first line on screen, code "22"h indicating, e.g., character of the standard size, and code "21"h indicating, e.g., small letter of alphabet are respectively assigned to data #1, (OPC), data #2 (OPR), data #3 (SSDA), data #4 (DSDA), data #5 (OPC), data #6 (OPR1). data #7 (OPR2), and data #8 (OPR3) are assigned.
Then, VTR detects presence or absence of so called a carrier on the bi-directional bus to transmit this frame P1 when there is no carrier, i.e., the bi-directional bus is empty, thereafter to once stop sending of carrier to open the bi-directional bus. Thus, VTR informs TV that data is transmitted at subsequent frame, carries out a control to lock TV, and informs kind (attribute) of data. It is to be noted that SSDA and DSDA are assigned according to need. For example, in communication from sub-device to device, DSDA is unnecessary. In communication from device to sub-device, SSDA is unnecessary. In addition, in communication from device to device, SSDA and DSDA are unnecessary.
Then, VTR forms, as shown in FIG. 4B, a frame P2 in which master address bits, slave address bits and control bits are caused to be respectively address of VTR, address of TV and code "B"h indicating data communication command, and data of, e.g., 32 bytes at the maximum are assigned to data #1, #2, #3 . . . to transmit this frame P2 when the bi-directional bus becomes empty for a second time. This operation is continued until a line displayed is changed.
Then, VTR transmits, as shown in FIG. 5A, in order to give an instruction of line change, a frame P3 in which master address bits, slave address bits and control bits are caused to be respectively address of VTR, address of TV and code "A"h (control command communication command), and code "EO"h (control command of display), code "21"h indicating, e.g., second line on screen, code "21"h indicating, e.g., capital of alphabet are respectively assigned to data #1 (CPC), data #2 (OPR1), data #3 (OPR2) and data #4 (OPR3) to subsequently transmit, as shown in FIG. 5B, a frame P4 in which master address bits, slave address bits and control bits are caused to be respectively address of VTR, address of TV and code "B"h (data communication command), and the remaining data are assigned to data #1, #2, #3 . . . .
Thereafter, VTR transmits, as shown in FIG. 5C, a frame P4 in which master address bits, slave address bits and control bits are respectively address of VTR, address of TV and code "E"h (control command communication command), and end command (code "BE"h) indicating that communication is completed is assigned to data #1 (OPC) to inform TV that communication of data has been completed, and to carry out a control to release lock of TV. Thus, transmission of data from VTR to TV is completed. TV displays character, etc. based on this data.
On the other hand, even in the case where data quantity of data to be transmitted is less than data capacity of the data field 105 and data to be transmitted can be transmitted by one frame, in the conventional bi-directional bus system, in order to inform that data is transmitted at subsequent frames, a frame in which control bits are caused to be control command communication command is transmitted thereafter to transmit a frame including data thereafter to transmit a frame in which control bits are caused to be control command communication command in order to inform a device on the receiving side that communication has been completed.
Namely, VTR transmits frame P1 (not shown) in which master address bits, slave address bits and control bits are caused to be respectively address of VTR, address of TV and code "A"h (control command communication command), and OPC "Begin 2", code "54"h address of video deck, address of TV monitor, code "EO"h, code "20"h, code "22"h and code "21"h are respectively assigned to data #1 (OPC), data #2 (OPR), data #3 (SSDA), data #4 (DSDA), data #5 (OPC), data #6 (OPR1), data #7 (OPR2) and data #8 (OPR3), thus to inform TV that this communication is communication of data.
Then, VTR transmits a frame P2 in which master address bits, slave address bits and control bits are caused to be address of VTR, address of TV and code "B"h (data communication command), and data are assigned to data #1, #2, #3 . . . .
Thereafter, VTR transmits frame P3 in which master address bits, slave address bits and control bits are caused to be respectively address of VTR, address of TV and code "E"h (control command communication command), and code "BE"h (end command) indicating that communication of data is completed is assigned to data #1 (OPC), thus to inform TV that communication of data has been completed.
As stated above, in the conventional bi-directional bus system, a source device e.g., VTR forms frames in sequence in accordance with the flowchart shown in FIG. 6 to transmit data.
At step ST1, VTR forms a data setting frame indicating that data is transmitted at subsequent frame to transmit this frame to TV. Then, the operation proceeds to step ST2.
At the step ST2, VTR sets control bits to data communication command. Then, the operation proceeds to step ST3.
At the step ST3, VTR judges whether or not a data quantity X is greater than data capacity n. If so, the operation proceeds to step ST4. If not so, the operation proceeds to step ST6.
At step ST4, VTR forms a frame including n data to transmit this frame. Then, the operation proceeds to step ST5.
At the step ST5, VTR subtracts data capacity n from data quantity X and allows a value obtained by subtraction to be new data quantity, i.e., calculate the remaining data quantity X. Then, the operation returns to the step ST3.
On the other hand, at step ST6, VTR forms a frame including data having data quantity X less than data capacity n to transmit this frame. Then, the operation proceeds to step ST7.
At the step ST7, VTR forms a frame for end command indicating that communication of data is completed to transmit this frame. The operation is completed.
As stated above, in the bi-directional bus system, before actual data is transmitted, a frame for informing a device on the receiving side that data is transmitted at subsequent frames is required, and a frame for informing the device on the receiving side that communication of data is completed at the time point when transmission of data is completed is required, resulting in the problems that the traffic quantity is increased, the transmission efficiency is low, and the communication procedure (protocol) is complex, etc.
Further, in the case where equipments of different makers (manufactures) are connected through a bi-directional bus to carry out data transmission therebetween, standardization of data is required. For example, as described above, in the case of displaying status of VTR on TV, it is necessary to decide language displayed, No. of languages of display, place of display, color of display, or the like. On the other hand, makers have a desire to transmit peculiar data (hereinafter referred to as arbitrary data) for equipments manufactured by themselves to add any value to those equipments, or to exhibit characteristics. However, in the conventional bus system, there was the problem that there is no technique for discriminating between standardized data and arbitrary data.